High resolution micro-CT scanners are becoming widely used for in vivo imaging of small laboratory animals. However, imaging of chest area remains a challenging task due to periodic respiratory and cardiac motion, where respiratory motion dominates. To reduce motion artifacts and to allow dynamic imaging, we propose a retrospective
synchronization method for scans of chest area in our in vivo micro-CT scanners. In this synchronization method, we acquire projection images in a step-and-shoot mode, where multiple images are acquired covering more than one motion cycle at each step with exact time marks of every acquisition. In the meanwhile motion signals are recorded. An offline sorting program has been developed to sort images into corresponding motion phases. We have evaluated our method on respiratory motion. Compared to prospective synchronization methods, our method has several advantages: 1. flexible in
sorting; 2. continuous imaging: maximum utilization of radiation dose applied to the animal; 3. possibility for 4D dynamic imaging; 4. can be used during irregular breathing cycle. This method has been applied to two of SkyScan in-vivo scanners. Initial results indicate that the proposed method is adequate.